In the past, there has been proposed a device configured to suppress an excess increase in a temperature of a light emitting diode (hereinafter referred to as “LED”) when operated, so as to keep it in a stable state, in order to stabilize a light output and a lifetime of the LED. For example, such a device is disclosed in document 1 (Japanese Unexamined Patent Application Publication No, 2010-272472).
An LED lighting apparatus disclosed in document 1 includes a lighting body and a liquid-cooled heat dissipation mechanism. The lighting body includes an LED light source, a temperature detection device, and a water-cooling jacket for cooling the LED light source. The liquid-cooled heat dissipation mechanism cools, by use of a radiator, a liquid coolant which absorbs heat from the LED light source when passing through the water-cooling jacket. With regard to this LED lighting apparatus, in the lighting body, to suppress an excess increase in the temperature of the LED light source when operated, the LED light source is operated by use of a control current corresponding to a detection temperature from the temperature detection device.
However, in the above prior art, when the LED light source operates abnormally for example, there is a possibility that the detection temperature deviates from an actual temperature by more than an allowable value. In this case, it is hard to adjust the temperature of the solid state light emitting device appropriately, and therefore the temperature of the solid state light emitting device is likely to exceed an allowable temperature of the solid state light emitting device. This may disadvantageously cause deterioration of a light emitting efficiency and shorten a lifetime of the solid state light emitting device.